Carbon black reactor with axial flow burner

ABSTRACT

An improved burner for combusting gaseous fuel and oxidant gas is provided in which the fuel and oxidant gas are premixed prior to combustion by the turbulence generated by flowing the gases through a mixing zone containing a centrally disposed flow disrupting bluff body positioned in the oxidant gas stream upstream from the point of fuel injection, and a peripheral flow disrupting bluff body disposed at the periphery of the mixing zone. The burner finds particular utility in combination with other elements of a furnace-type carbon black reactor. This abstract is not to be construed in any way to define or limit the invention set forth below.

BACKGROUND OF THE INVENTION

This application is a division of co-pending application Ser. No.711,443 filed Aug. 4, 1976 now Pat. No. 4,077,761 issued Mar. 7, 1978.This invention relates to an improved method and apparatus for gaseousfuel combustion, useful in many applications. This invention alsorelates to the production of furnace-type carbon black, utilizing a hotstream of gases produced by the burner apparatus of the invention, andinjecting into the hot gases a suitable feedstock hydrocarbon underproper flow conditions. More particularly, the invention relates to animproved method and apparatus for producing carbon black whereby heat isgenerated in an especially advantageous manner and in which theconditions of flow of the hot gases and the manner of introduction ofthe hydrocarbon feedstock are such as to allow a highly desirableversatility in the production of a wide range of particle size andstructure of furnace carbon blacks demanded by the market.

Carbon blacks are produced by several processes, the most common beingthe channel process, the thermal process and the furnace process. Thehistoric channel process produces carbon black by the impingement offlames of gaseous fuel on channel irons in an environment of airdeficiency. Because of the price and supply of natural gas, the processis much less used than formerly. The thermal process is a cyclic processwhich contacts hydrocarbon gases cyclically with hot checkerwork, andproduces a coarse carbon black of low structure. The thermal blacks areused largely as fillers where a minimum of reinforcement of rubber isrequired. The furnace process is more economical than these two. In thefurnace process, a hydrocarbon fuel is burned in a closed vessel,usually refractory-lined, to produce hot combustion product gases andanother hydrocarbon stream is injected into the hot gases of combustionto be carbonized and form the product. The second hydrocarbon streamfrom which the carbon black is made is commonly referred to as the"make" or "feedstock" stream.

In the furnace processes, the feedstock may be a gas, but for botheconomic and quality reasons, an aromatic hydrocarbon oil is thematerial of choice. The fuel may be a gas or an oil, but where gas isavailable and is economical, it is the fuel of choice.

Oil furnace carbon black reactors are generally of circular crosssection and elongate configuration, and are functionally composed ofseveral zones. The first zone is the zone of combustion in which fueland air are burned to produce hot combustion product gases which supplyheat for the process. This heat-supplying combustion process is ofcritical importance, because the temperature of the combustion productsdetermines to a great degree the quality of the carbon black produced.In addition, a combustion system which results in uneven burning maycause marked and harmful temperature gradients within a reactor, thussubjecting one portion of the feedstock to a different temperature thananother portion of the feedstock. Unburnt fragments of a non-aromaticfuel may also interfere with the kinetics of carbonization of thearomatic oil. It is also important that the hot gases leaving the zoneof combustion flow in such a manner that the aerodynamic pattern isfavorable to the formation of the quality of carbon black desired.

The most efficient burners heretofore known for carbon black reactorsutilized vortex or tangential flow of the gases in order to achievesufficient mixing of the air and fuel gas for complete, uniformcombustion. However, a characteristic of such a burner is that the hotcombustion products continue to have a vortex, or tangential flow,pattern as they exit from the burner and enter the carbon black reactorproper. This is less desirable for the production of certain types ofcarbon black than is axial or linear flow of the reaction products. Onthe other hand, linear flow of the combustion product gases, wheredesired, has heretofore been achieved only through burners which areless efficient and advantageous than either vortex burners or theburners of the present invention. Therefore, combination of the burnerof the present invention, with the other elements of a carbon blackreactor, as hereinafter described, provides for highly efficientcombustion of the fuel gas and air while at the same time producinglinear or axial flow of the combustion products as they are fed to thereaction zone of the carbon black reactor.

The second zone in the reactor is the zone of reaction, in which the oilis dehydrogenated, nucleated as carbon, accreted into chains or clustersto form what is known as structure, and formed into the ultimateparticle size it will attain. In the electron microscope, carbon blacktypically appears as more or less spheroidally-shaped particles fusedtogether in clusters or chains. The degree of such clustering orchaining is the degree of structure of the material. When compoundedinto rubber formulations, blacks with higher structure produce stiffercompounds, and may be compounded with higher proportions of extenderoil, which is an economic advantage. In some degree, higher structurecontributes to the resistance to abrasion of rubber used in treads ofautomobile tires. However, for some uses in rubber, lower levels ofstructure are required. Therefore, it is necessary that the manufacturerof carbon black be able to make a range of structure levels to meet themarket demands.

The third zone of the carbon black process is the quench zone in whichthe reaction is rapidly cooled by water injection. After the formationof the carbon, prolonged exposure to high heat damages the properties ofthe rubber formulations made with the product. The choice of theposition of the water stream which quenches the reaction may be properlymade by those skilled in the art of carbon black manufacture. Ifquenched too soon, the process will produce an oily carbon; if quenchedtoo late, the process will produce a black with a damaged surface.

OBJECTS OF THE INVENTION

One object of the invention is to provide a novel burner apparatus whichproduces a flame of high temperature and high heat release per unit ofvolume. Another object is to provide a burner producing a stable flamefront without flame contact with a flame holder. Another object of theinvention is to provide apparatus for producing a stable, intense flamewithout introducing fuel or oxidant gas tangentially to form a vortexand for obtaining the quality of combustion attainable by tangential orvortex flow, without utilizing tangential flow or the ponderousequipment which its use requires.

An important object of the invention is to provide a combination of auniquely efficient non-tangential burner of great flexibility with atapered carbon black reactor, including means for radial injection ofcarbon black feedstock into the axially flowing combustion products inthe reactor.

DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will becomeapparent from the specification drawings and claims. In the accompanyingdrawings, in which like numerals indicate like parts:

FIG. 1 is a view in vertical section illustrating, somewhatdiagrammatically, a preferred embodiment of the burner according to thepresent invention;

FIG. 2 is a view in front elevation of the central bluff body of theburner of FIG. 1;

FIG. 3 is a view in side elevation of the central bluff body of FIG. 2;

FIG. 4 is a view in vertical section illustrating diagrammatically thefunction of the burner of FIG. 1 when the central bluff body is locatedupstream of the annular bluff body;

FIG. 5 is a view in vertical section illustrating diagrammatically analternate embodiment of the burner, having a plurality of central andannular bluff bodies;

FIG. 6 is a view in vertical section illustrating the preferredcommercial embodiment of the burner;

FIG. 7 is a view in front elevation of the peripheral bluff body of FIG.6;

FIG. 8 is a view in vertical section of the peripheral bluff body ofFIG. 7, taken along lines 8--8 of FIG. 7; and

FIG. 9 is a view in side elevation of a furnace-type carbon blackreactor in combination with the burner of FIG. 6.

DESCRIPTION OF THE INVENTION

Referring to FIG. 1 there is shown in vertical section a burner 10constructed in accordance with the present invention. It includes acylindrical housing 12, preferably of metal, defining a generallycylindrical mixing zone 14, in which the oxidant gas and fuel arepremixed, and a combustion zone 16 in which the gases are burned torelease heat. The housing 12 is of enlarged diameter as shown in 12a inthe combustion zone area and is lined with refractory material 18 totolerate high temperatures produced by the burner. A plate 20 attachedto housing 12 by flange 22 closes the upstream end of the mixing zone14.

Means for introducing oxidant gas, preferably air, into the mixing zone14 comprise a duct 24 opening through the housing 12 and having a flange26 for attachment to a supply of oxidant gas, preferably air. Airsupplied through duct 24 will flow axially through the mixing zone 14,where it is admixed with gaseous fuel as described hereinbelow, andthence into the combustion zone 16 for combustion.

Means for introducing gaseous fuel into the air flowing axially in themixing zone 14 preferably comprise a fuel supply tube 28 connected tofuel supply 30 and having a plurality of orifices 32 for injecting fuelgas into the flowing oxidant gas at a point downstream from the airsupply duct 24. The fuel supply tube 28 is centered about thelongitudinal axis of the mixing zone 14 in housing 12 and extendsthrough a central opening 34 in the end plate 20. Tube 28 is manuallyadjustable along the longitudinal axis of the mixing zone 14, a suitablepacking gland 36 permitting such axial adjustment of the fuel supplytube while retaining a seal to prevent escape of gas from the burner.

Means for centering the supply tube in the mixing zone include threeadjustment bolts 38 which extend through nuts 40 mounted on the burnerhousing 12, and through openings in the housing, to engage the outsidesurface of the supply tube 28. One bolt 38 is provided for verticaladjustment of the supply tube 28 and two additional bolts disposed onopposite sides of the tube 28 permit horizontal adjustment.

Means are provided for admixing the air and fuel in the mixing zone 14prior to their admission into the combustion zone 16. These mixerscomprise a central bluff body 42 centered about the longitudinal axis ofthe mixing zone 14 and extending radially outwardly and a peripheralbluff body 44 spaced axially from the central bluff body and disposedabout the periphery of the mixing zone 14, extending radially inwardlyfrom the periphery toward the central longitudinal axis.

By the term "bluff body" as used herein is meant a non-streamlined,flow-interrupting body which is preferably, although not necessarily, ofsquare-edged generally circular configuration and which causes mixingturbulence in the gases flowing in the burner.

As shown in greater detail in FIGS. 2 and 3, the central bluff body 42preferably comprises a square cornered annular plate 46 mounted on thefuel supply tube 28 upstream from the orifices 32. The plate has aninside diameter approximately equal to the outside diameter of the gassupply tube 28 and an outside diameter substantially less than thediameter of the mixing zone 14, whereby oxidant gas may flow freelythrough the annular space defined by the inside diameter of the burnerbody 12 and the outside diameter of the plate 46.

Means are provided for mounting the plate 46 on the fuel supply tube 28and for permitting its longitudinal adjustment with respect to orifices32. Such mounting and adjustment means preferably comprise a pluralityof nuts 48 welded edgewise to the plate 42 for receiving bolts 50 whichmay be selectively tightened to rigidly mount the plate 46 on the supplytube 28 and loosened to permit plate 46 to be adjusted longitudinally ofthe supply tube 28, with respect to the fuel orifices 32.

The peripheral bluff body 44 comprises a square-edged annular plate 52having an outside diameter approximately equal to the diameter of themixing zone 14 and a central opening 54 which permits the mixture offuel and air to flow therethrough into the combustion zone 16. The plate52 may be made of metal or other suitable material capable ofwithstanding high temperatures.

In operation of the burner, oxidant gas, preferably air, is suppliedthrough duct 24, as indicated by arrows 56 and flows axially through themixing zone 14 of the burner. Gaseous fuel, preferably natural gas, issupplied through tube 28 and exits from the orifices 32 in a generallyradial direction, as indicated by the arrow 58. A mixing turbulencebetween the air and fuel is created, as indicated at 60, as the airflows around the central bluff body 42. An additional mixing turbulence,as indicated at 62, is caused as the air and fuel flow around theperipheral bluff body 44. Combustion takes place downstream of theperipheral bluff body 42 in the combustion zone 16 and remains stable,without the necessity for a flame holder.

As will be understood by those skilled in the art, various adjustmentsin the size, shape and relative positions of the central and peripheralbluff bodies, and of the position of the fuel orifices 32 with respectto the bluff bodies, may be necessary in order to provide stable,complete combustion under the various conditions of air to fuel ratios,BTU content of the fuel, oxygen content of the oxidant gas, air and fuelsupply rates, pressures, temperatures, etc. Depending upon anyparticular combination of variables present, some degree ofexperimentation may be required in order to produce optimum results, andit is for this reason that the bluff body 42 is preferably madeadjustable with respect to the gas orifices 32, and the assemblycomprising the gas tube 28 with its holes 32 and the attached bluff body42 is axially adjustable with respect to the peripheral bluff body 44.

While the central bluff body 42 is always maintained upstream from thegas supply orifices 32, the gas supply orifices and/or the central bluffbody 42 may be positioned either upstream of the peripheral bluff body44 (as indicated in FIG. 1) or downstream thereof (as indicatedschematically in FIG. 4) in order to maintain optimum combustion. Also,it may be desirable to use a plurality of central bluff bodies 42 andperipheral bluff bodies 44 as illustrated in FIG. 5. In this event, itis desirable to provide a separate set of gas supply orifices for eachof the central bluff bodies.

It has been found that positioning the gas supply orifices 32 andcentral bluff body 42 upstream of the peripheral bluff body 42 ispreferable where the supply air is preheated to about 350° F or higher.However, where ambient temperature supply air is utilized, more stablecombustion is generally achieved by positioning the central bluff bodyand gas supply orifices downstream of the peripheral bluff body, asillustrated in FIG. 4.

Combustion takes place downstream of the peripheral body 44 which doesnot function as a flame holder; however, since it is subjected toradiant heat, it is preferably made of heat resistant material, as forexample, heat resistant alloy. As hereinafter explained, a design may beused in which the peripheral bluff body is cooled by a small flow ofcombustion air.

In the preferred commercial embodiment of the burner, illustrated inFIG. 6 of the peripheral bluff body is formed of metal plate and coolingmeans are provided.

As shown in greater detail in FIG. 6 through 8, the peripheral bluffbody 44 of the preferred commercial embodiment comprises an annularplate 64, preferably of metal, of slightly less outside diameter thanthe diameter of the mixing zone 14 and having a sufficient centralopening 66 to permit the mixture of oxidant gas and fuel to flow therethrough into the combustion zone 16. The annular plate 64 is centeredin the mixing zone by means of a cylindrical support member 68 mountedon an annular flange 70 which fits between flanges 72 provided in theburner body 12. Bolts 74 extend through aligned openings in the flanges70 and 72.

Mounting flange 70 has an inside diameter approximately equal to that ofthe supporting cylinder 68 for annular plate 64, thereby providing acentral opening 76 through the flange 70 equal in diameter to the insidediameter of cylinder 68, through which opening 76 the air-fuel mixturemay flow toward the annular plate 64, and through which the fuel supplytube 28 may extend into the cylinder 68, as illustrated in FIG. 6. Aplurality of openings 78 are provided about the periphery of mountingflange 70 whereby supply air may circulate through the annular space 80between the inside diameter of the burner body 12 and the outer surfaceof the support cylinder 68, thereby cooling the surface of the cylinder68, which acts as a heat sink for the annular plate 64. If desired, aplurality of openings 82 may also be provided in the body of thesupporting cylinder 68 to provide for additional gas circulation intothe annular space 80.

A burner constructed substantially in accordance with FIG. 6, butlacking the central bluff body 42, has been commercially used for someperiod of time in connection with carbon black manufacture. However,this burner was generally unsatisfactory in that the distribution oftemperatures in the combustion zone 16, from highest temperature tolowest in the zone, was too wide, indicating incomplete mixing of thesupply air and fuel gas prior to combustion and also indicatingincomplete combustion of the fuel. Also, under certain flow conditions,the burner was subject to severe and potentially destructive sonicvibrations. However, upon modification of the burner by addition of thecentral bluff body 42, combustion temperatures in zone 16 became moreuniform, fuel combustion more complete and the destructive sonicvibrations were eliminated.

While the burner of the present invention may find utility in a varietyof commercial and industrial applications, it is particularly useful asthe burner section of a furnace-type carbon black reactor for thereasons stated in the Background of the Invention section above.

Referring now to FIG. 9, there is shown a burner 10 according to thepresent invention in combination with a carbon black reactor 84including an outer housing 86, preferably of metal, lined with arefractory material 88 of varying thickness to provide a centrallongitudinal tunnel 90 of generally circular cross-sectionalconfiguration and varying diameter. The reactor tunnel 90 includes acombustion zone 92 in which the admixed air and fuel gas from the burner10 are combusted to produce high temperature combustion products whichflow axially through the combustion zone to a reaction zone 94comprising a convergent section 94a and divergent section 94b. Aplurality of ports 96 extend through the housing 86 and refractory 88 ofthe reactor to provide access for feedstock supply tubes 98 throughwhich hydrocarbon feedstock, preferably oil, is injected radially fromnozzles 100 into the hot flowing combustion product gases in theconvergent section 94a of the reactor. Although two feedstock injectiontubes 98 are illustrated, any desired number may be utilized, disposedradially about the reactor. The feedstock injection tubes are adjustableradially with respect to the longitudinal axis of the reactor 84 so thatthe degree of radial penetration of the injection nozzles 100 into thereactor zone of the reactor may be controlled as desired. Also, aplurality of feedstock supply ports 96 are provided, spaced axiallyalong the reactor, so that the feedstock supply may be selectivelypositioned as desired along the axis of the reactor. Feedstock injectionports not in use are closed by plugs 102.

The pyrolysis reaction commenced as the atomized feedstock oil isinjected into the axially flowing hot gases from the burner 10 bynozzles 100 continue as the combustion gases and oil droplets movethrough the convergent and divergent portions of the reaction zone 94and into the quench zone 104 in which the reactions are quenched byquench water 106 supplied through nozzle 108 from pipe 110. Theresulting mixture of gases and carbon black product then exits thereactor to a suitable collection system (not shown) downstream, in whichthe product is separated from the combustion product gases and steam andis subsequently pelletized and packaged.

The foregoing disclosure and description of the invention and of thepreferred embodiments is illustrative and explanatory thereof only andvarious changes may be made in the size, shape and materials ofconstruction without departing from the spirit of the invention.

What is claimed is:
 1. An apparatus comprising:a carbon black reactorlined with refractory material of varying thickness defining alongitudinal tunnel of generally circular cross-sectional configurationand varying diameter, said tunnel comprising combustion, reaction andquench zones; a burner for supplying admixed oxidant gas and gaseousfuel to the combustion zone of said carbon black reactor for combustiontherein to provide hot combustion product gases for flowing through saidreactor to produce carbon black, said burner comprising, a housingdefining a generally cylindrical mixing zone having a central axisextending longitudinally therethrough, said mixing zone being in opencontiguous axial alignment with the combustion zone of said carbon blackreactor, means for introducing oxidant gas into said mixing zone to flowaxially therethrough, means for introducing gaseous fuel into saidmixing zone at a point downstream of said oxidant gas introductionmeans, whereby said fuel is released into said flowing oxidant gas,mixer means in said mixing zone for admixing said oxidant gas and fuel,said mixer means comprising, a central bluff body centered about theaxis of said mixing zone and extending radially outwardly from saidaxis, and a peripheral bluff body disposed at the periphery of saidmixing zone and extending radially inwardly toward said axis, saidcentral and peripheral bluff bodies being spaced axially from eachother; means for introducing liquid hydrocarbon feedstock radially intosaid reactor zone of said carbon black reactor; and means forintroducing quench water into said quench zone of said carbon blackreactor.
 2. The apparatus according to claim 1 wherein said reactionzone includes convergent and divergent portions.
 3. The apparatusaccording to claim 1 wherein said means for radially injecting saidfeedstock into said reaction zone are adjustable both radially andaxially with respect to said combustion zone.
 4. The apparatus accordingto claim 1 wherein a plurality of central bluff bodies and a pluralityof peripheral bluff bodies are provided spaced axially along said mixingzone.